In recent years, the capacity of storage batteries has been greatly increased, and the utilization of storage batteries, for example, for driving electric vehicles such as electric automobiles and electric motor bikes and for storing power consumed in homes, stores, buildings and the like has been examined; it is expected that storage batteries will be wildly used in the future.
Although storage batteries supply power by discharge, it is necessary to perform charge before discharge. Hence, when a storage battery often performs discharge to supply power, it is necessary to often charge the storage battery. For example, in patent document 1, a power supply system is proposed that includes a solar battery and a storage battery which is charged with power generated by the solar battery. In the power supply system described above, when the storage battery is fully charged, the charge is stopped, and the power that has been so far utilized for the charge and generated by the solar battery is instead utilized for cooling the storage battery. In this way, it is possible to decrease the temperature of the storage battery immediately after the full charge and to bring, in a short time, the storage battery into the state where it can be charged, without the waste of the power generated by the solar battery.